Described herein are porous microspheres having a size of from about 3 to about 50 microns and a narrow particle size distribution. Also described is an emulsion aggregation method for making such porous microspheres.
There are numerous applications for porous microspheres in chemistry, biochemistry and environmental engineering, including use in ion-exchangers, adsorbents and separation media. There is also a significant amount of biochemical research that benefits from the use of porous microspheres.
There has been an increasing interest in porous polymer particles in recent years. Especially, styrene-acrylate copolymers have been used as precursors for ion-exchangers, adsorbents and GPC column materials. Crosslinked polymer particles with a permanent macroporous structure are efficient materials for many separation processes. The macropores of the particles allow biomolecules, for example in the general size of 500,000 dalton, to be separated.
The preparation of porous microspheres in the size range of about 3 to about 50 microns with narrow particle size distributions is often difficult and expensive. Existing methods of preparing these materials are limited and often involve the use of size classification. Size classification is time consuming and wasteful, as a large percentage of the microspheres must be discarded as being too large or too small.
Porous polymer microspheres may be produced by suspension polymerization by adding an inert diluent to the polymerizing mixture. After polymerization, the inert diluent is removed, leaving a porous structure within the polymer particles. The suspension process gives relatively large particles (100-10,000 μm) with a broad particle size distribution, which is disadvantageous with regards to flow conditions, separation and packing efficiency. It is expected that the improved separation efficiency, optimal packing and lower backpressure can be achieved with narrower particle size distribution macroporous polymer particles as compared to polydisperse separation media.
U.S. Pat. No. 6,841,580 describes an organic porous material having a continuous pore structure, which comprises interconnected macropores and mesopores with a radius of 0.01 to 100 microns in the walls of the macropores, having a total pore volume of 1 to 50 ml/g and having pore distribution curve characteristics wherein the value obtained by dividing the half-width of the pore distribution curve at the main peak by the radius at the main peak is 0.5 or less. The organic porous material is useful as an adsorbent having high physical strength and excelling in adsorption amount and adsorption speed, an ion exchanger excelling in durability against swelling and shrinkage, and a filler for chromatography exhibiting high separation capability. See the Abstract.
A simple and economical process for preparing porous microspheres in the size range of from about 3 to about 50 microns that allows for control of size distribution is desired.